Problem 77 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Write balanced equations for the following reaction : Acetamide is reacted with bromine in the presence of potassium hydroxide.

Step-by-Step Solution

Answer

The balanced equation is: \( \text{CH}_3\text{CONH}_2 + \text{Br}_2 + 4\text{KOH} \rightarrow \text{CH}_3\text{NH}_2 + 2\text{KBr} + \text{K}_2\text{CO}_3 + 2\text{H}_2\text{O} \).

Step 1: Identify the Reactants and Products

In the given problem, acetamide \((\text{CH}_3\text{CONH}_2)\) reacts with bromine \((\text{Br}_2)\) in the presence of potassium hydroxide \((\text{KOH})\). The reaction results in the formation of methylamine \((\text{CH}_3\text{NH}_2)\), potassium bromide \((\text{KBr})\), potassium carbonate \((\text{K}_2\text{CO}_3)\), and water \((\text{H}_2\text{O})\).

Step 2: Write the Unbalanced Equation

Write down the chemical equation showing the reactants and products: \[ \text{CH}_3\text{CONH}_2 + \text{Br}_2 + \text{KOH} \rightarrow \text{CH}_3\text{NH}_2 + \text{KBr} + \text{K}_2\text{CO}_3 + \text{H}_2\text{O} \]

Step 3: Balance the Equation I - Balance Complex Ions and Atoms

First, focus on balancing the main organic reactant and product (acetamide and methylamine, respectively). Here, these are already balanced. Next, potassium (K), bromine (Br), and more complex ions will need balancing.

Step 4: Balance Potassium and Bromine Atoms

Ensure the number of potassium and bromine atoms are equal on both sides. Since there are 2 bromine atoms in the reactants from bromine \((\text{Br}_2)\), we need 2 moles of potassium bromide \((\text{KBr})\) in the products.

Step 5: Balance Oxygen and Hydrogen Atoms

Adjust the equation so the number of oxygen and hydrogen atoms is the same on both sides. Adding 2 more moles of water \((\text{H}_2\text{O})\) can balance the equation further, since there are additional OH ions from 4 moles of KOH.

Step 6: Final Balanced Equation

Having adjusted for each component, the balanced equation becomes: \[ \text{CH}_3\text{CONH}_2 + \text{Br}_2 + 4\text{KOH} \rightarrow \text{CH}_3\text{NH}_2 + 2\text{KBr} + \text{K}_2\text{CO}_3 + 2\text{H}_2\text{O} \]

Key Concepts

Balanced Chemical Equations

Balancing chemical equations is an essential skill in chemistry that ensures the law of conservation of mass is respected. In practice, this means the number of each type of atom on the reactant side (the starting substances) must equal the number on the product side (the substances formed). Let's look at an example where acetamide reacts with bromine in the presence of potassium hydroxide to form several products, including methylamine.

• Start by identifying all the reactants and products in the chemical reaction.
• Write down the unbalanced chemical equation with all the reactants on the left side and the products on the right.
• Begin balancing the equation via the most complex molecules first, often the organic compounds or those that appear less frequently.
• Next, balance the metals, followed by non-metals.
• Finally, leave hydrogen and oxygen atoms to be balanced last, as they are often found in multiple compounds.

In the specific case of acetamide reaction, balancing was achieved by ensuring each type of atom present had equal amounts on both sides, ultimately yielding the balanced equation:\[ \text{CH}_3\text{CONH}_2 + \text{Br}_2 + 4\text{KOH} \rightarrow \text{CH}_3\text{NH}_2 + 2\text{KBr} + \text{K}_2\text{CO}_3 + 2\text{H}_2\text{O} \]This meticulous process ensures that no atoms are lost or gained during the chemical reaction.

Reaction Mechanisms

Chemical reactions often follow specific step-by-step paths known as reaction mechanisms. Understanding these mechanisms helps chemists predict how reactants will interact to form products. They can illustrate details like intermediate steps or how bond-making and bond-breaking occurs.
A reaction mechanism is typically explained by breaking down a chemical equation into several elementary steps, which may involve short-lived intermediate species.

• Each step can involve the transfer or sharing of electrons, new chemical bonds forming, or existing bonds breaking.
• The rate of the overall reaction may depend on one or more of these steps, often called the rate-determining or slowest step.
• By analyzing these details, chemists can propose pathways that highlight the molecular rearrangements and provide insights into why certain products form.

In organic chemistry, understanding reaction mechanisms is especially critical. For instance, in the reaction involving acetamide, bromine, and potassium hydroxide, exploring the mechanism would clarify how methylamine is formed from acetamide and how potassium ions react with other products. Such knowledge informs how we can manipulate conditions to steer the reaction towards desired products efficiently.

Organic Chemistry Reactions

Reactions within organic chemistry often involve compounds with carbon backbones and unique functional groups, like amides, alcohols, or ketones. Understanding these reactions is crucial due to the variety of substances and compounds involved in real-life applications, including pharmaceuticals and polymers.
The reaction involving acetamide is an excellent example of organic chemistry in action. Here, acetamide (an amide) reacts with bromine in the presence of a strong base, potassium hydroxide, leading to the formation of methylamine:

• Organic reactions commonly involve the transformation of specific functional groups. For instance, converting the CONH₂ group of acetamide to the NH₂ group in methylamine.
• These transformations are crucial for synthesizing new organic compounds and require careful manipulation of reaction conditions.
• Reactants, like bromine in this scenario, often serve as oxidizers or sources of 'halogen' to facilitate certain transformations.

This type of reaction is part of a larger class of organic transformations and highlights the versatility and creativity inherent in organic chemistry, paving the way for synthesizing a wide range of complex molecules.